This invention relates to methods and apparatus for producing television images perceived by viewers to be stereoscopic.
Conventional stereoscopic television systems typically require special viewing aids, such as polarized glasses or ones having colored lenses, or special receiving equipment. Typical of the latter approach is the method for producing a three dimensional television image by alternating pictures from stereoscopic television cameras described by Carrillo in U.S. Pat. No. 3,457,364. The method of Carrillo requires a special picture tube for color. In addition, my tests indicate that the alternation method described by Carrillo (approximately 60 alternations per second, 30 of each picture, synchronized to the television field rate) may produce less depth illusion than methods using lower alternation rates.
In U.S. patent application Ser. Nos. 66,722 filed Aug. 25, 1970 and 308,209 filed Nov. 20, 1972, I described a method to produce the desired three dimensional effect while maintaining compatibility with existing broadcast standards and existing home TV receivers. However, when the two stereoscopic cameras are converged on foreground objects, in accordance with that method, background objects sometimes appear to flicker and jump. Similary, when the cameras are pointed at background objects, foreground objects may appear to flicker and jump. The main contributor to this flicker and jump effect is the limit of binocular fusion of the visual perception process in combination with the flicker effect of the low alternation rate. The limit of binocular fusion phenomenon was first investigated by Panum in 1856 and is known to visual perception scientists as the limiting case of the Panum Phenomenon as disclosed in Rosenblith, Walter A. (editor), Sensory Communication, John Wiley & Sons, 1961, which discusses, in chapter 32, the physiological basis for the perception of binocularly fused images as a result of the alternation of stereo images and which is incorporated herein by reference in its entirety.
Efforts to reduce the detrimental effects of this limit of binocular fusion while still maintaining a three dimensional effect produced my invention described in U.S. Pat. No. 4,006,291. But the method of this invention did not completely correct the problem since it is designed to minimize the effects but does not correct or remove the cause.
The method of Carrillo does not have a flicker problem since the alternation rate is far above the critical flicker frequency described in visual perception literature. However, the limit of binocular fusion problem manifests itself as a double image.